At Liberty University, he delves deeply into religion and urges listeners to look beyond differences they might have with his Mormon faith.

LYNCHBURG, Va. — When it came to evangelicals in this year's primaries, Mitt Romney was most often the rejected suitor — struggling to overcome suspicions about his authenticity as a conservative and his Mormon faith.

On Saturday at the evangelical university founded by the late televangelist Jerry Falwell in Lynchburg, Romney tried to tackle those lingering misgivings as the presumed Republican nominee — by delivering a speech that delved deep into his faith and by urging about 30,000 in the audience at Liberty University to look beyond their differences with his religion.

"People of different faiths, like yours and mine, sometimes wonder where we can meet in common purpose when there are so many differences in creed and theology," Romney said, alluding to the long-standing tensions between Mormons and evangelical Protestants, many of whom do not consider Mormonism to be part of the Christian faith. "Surely the answer is that we can meet in service, in shared moral convictions about our nation stemming from a common worldview."

The former Massachusetts governor took the stage after Chancellor Jerry Falwell Jr., quoting his father, noted that the American people would be "electing a commander in chief, not a pastor or a religious leader" in November.

Still, Romney dipped more deeply into the subject of religion than at any time since 2007, when he formally addressed his Mormon faith during a Texas speech, saying he was "an American running for president" and did not define his candidacy by his religion.

During his 20-minute address before about 6,000 black-robed graduates at Liberty's Williams Stadium, Romney mentioned God nine times. He praised Christian luminaries like abolitionist William Wilberforce, German theologian Dietrich Bonhoeffer and the Rev. Billy Graham. He sought to reassure his evangelical listeners of their shared conservative principles: his belief in the primacy of family, his opposition to gay marriage and his intent to champion religious liberty in a nation that "from the beginning," he said, "trusted in God, not man."

Citing the work of David Landes, a professor emeritus of economics at Harvard University, Romney argued that the central element of America's rise to global leadership "is our Judeo-Christian tradition, with its vision of the goodness and possibilities of every human life."

Romney received a standing ovation before and after his speech, and one line brought the entire crowd to its feet: his affirmation that "marriage is a relationship between one man and one woman" — a repudiation of same-sex marriage and of President Obama, who announced his support for gay marriage Wednesday.

Romney also credited former rival Rick Santorum — who trounced Romney among evangelicals in primary after primary — with helping to shape his thinking on what he called the "enduring institution of marriage" and the power of family values. Santorum, he said, had shared a Brookings Institution study showing that those who earn high school degrees, get full-time jobs and marry before having children have a far greater chance of financial success than those who don't.

"Culture — what you believe, how you live — matters," he said.

Romney's allies and detractors alike viewed Saturday's speech as a pivotal moment that would test the candidate's ability to inspire a group of voters that must organize on his behalf if he is to defeat Obama in key swing states like Virginia, North Carolina, Missouri, Florida and Ohio.

Even before the bruising primary season, a survey by the Pew Forum on Religion & Public Life late last year showed that Romney began at a disadvantage with that group. More than half of white evangelical Protestant Republicans surveyed said they did not view the Mormon religion as a Christian faith; 15% said Romney's Mormonism would make them less likely to vote for him.

When that uneasiness was paired with distrust of Romney's shift on abortion and gay rights, and his unpopular healthcare plan in Massachusetts, "You could almost draw a straight line down from the states with the fewest evangelical voters, where he did the best in Republican primaries, and those states where you have the largest proportion and he did the poorest," said Jim Guth, a political science professor at Furman University in Greenville, S.C., who specializes in the intersection of politics and religion.

Those results raised questions about whether Romney would be able to match the 73% of the evangelical vote won by 2008 Republican nominee John McCain — who had to overcome his 2000 critique of Falwell and fellow evangelist Pat Robertson as "agents of intolerance" — much less the 79% won byPresidentGeorge W. Bush in 2004.